In paper and paperboard manufacture, sheet formation is generally obtained on wire webs in a wet end from pulp slurry and is followed by the gradual removal of moisture in a press section and drier section. A calender section follows the drier section with the purpose of obtaining a desired finish (e.g. smoothness, thickness, gloss).
Despite the real advantages of using mechanical action to impart certain characteristics to the sheet, these advantages are limited. Complementary solutions for improving even further certain paper or paperboard characteristics can be applied internally in the wet end or externally with size-presses or coaters when these are available. These solutions are related to the use of fillers and functional additives.
Fillers are generally white pigments that can be divided in two major categories:    a) regular fillers having wide application and cost lower than that of cellulosic fiber, e.g. kaolin clay, ground calcium carbonate and precipitated calcium carbonate;    b) specialized fillers having usually lower volume applications and costs sometimes comparable with or even higher than cellulosic fiber; Some examples are: anatase titanium dioxide, rutile titanium dioxide, composite pigments, e.g. clay and titanium dioxide, PSS (precipitated synthetic silica—silica oxides and precipitated silicate—aluminum silicate), talc (industrial grade hydrated magnesium silicate), aluminum trihydrate, calcium sulfate, natural or precipitated barium sulfate, zinc oxide, zinc sulfur—surface treatments only, Satin White (calcium sulfo-aluminate complex)—surface treatments only, urea formaldehyde resin (organic pigment), plastic pigments (empty or full spheres)—surface treatments only.
The advantages brought by fillers in paper or paperboard manufacture are mostly related to cost reduction (except with some of the specialized fillers, especially titanium dioxide). The process disadvantages are however important and concern mostly wire, felt, doctor blade, refiners abrasion, machine deposits increase, increased Tinting dust, breaks related to sheet strength decrease and filler retention difficulties requiring retention program solutions.
On the other hand, the functional advantages (with respect to final product characteristic) brought by fillers are also important: optical properties (brightness and opacity) improvement, improved printability, better sheet formation, increased smoothness, improved dimensional stability. The functional disadvantages are mostly related to increased two sidedness, reduced rigidity, increased linting and decreased sheet strength.
As mentioned earlier improving the paper or paperboard characteristics beyond the mechanical limits of a paper or paperboard machine often requires the use of fillers for their functional advantages and the use of functional additives for even better results.
Examples of functional additives (which can improve the sheet characteristic) are dyes and optical brighteners, coating polymers, wet and dry strength resins, sizing agents, fluorocarbons and other specialty additives, while process additives (that improve the production process) are biocides, deposit-control agents, felt conditioners and cleaners, defoamers, and effluent treatments.
Sizing agents, opacifying agents, optical brighteners are important functional additives used to improve the sheet characteristics obtained with mechanical means and with filler use. Resistance to water penetration, better printing characteristics, increased opacity brightness and whiteness, increased bulk and caliper, better formation, were investigated and often obtained with one or several of these products. Some process improvements related to reduced abrasion, cost reduction, were also noticed in some cases.
Many compositions have been added to the slurry in an attempt to size the paper, i.e. render the paper water repellent. Most known sizes, such as those disclosed in U.S. Pat. No. 2,142,986 to Arnold, Jr. and U.S. Pat. No. 3,096,232 to Chapman, employ a type of wax. For example, Arnold Jr. discloses that an emulsion of wax in a solution of deacetylated chitin, paraffin waxes, Japan wax, carnauba wax, higher aliphatic alcohols, or synthetic waxes may be employed as the waterproofing agent in a sizing composition. A softening agent such as aliphatic alcohols containing 12 to 20 carbons is also present in the composition of Arnold, Jr. Chapman discloses the use of paraffin waxes or water-insoluble derivatives of resins for producing aqueous wax emulsions with cationic modified starches.
In U.S. Pat. Nos. 5,296,024 and 5,292,363 a papermaking composition is disclosed for enhancing opaqueness comprising the reaction product of a fatty acid and a diamine. Even if this composition is effective, there are still further improvements needed for strength of the paper, and coefficient of friction.
U.S. Pat. No. 2,772,967 Padbury et al shows a paper sized by adding thereto a salt of a high molecular weight composition prepared by reacting a dialkanolamine or trialkalonamine with a long chain fatty acid. The salt is diluated with water to form a dispersion containing a 5% concentration of sizing agent before being applied to the cellulosic fibers. Apparently, such a dilution of strength was necessary heretofore because until the present invention, preparation of the stearamides which would allow the composition to remain pourable at concentration greater than 5% was unknown. Without the ability to remain in an emulsion and, hence, be poured, concentration of stearamides approaching those disclosed therein had apparently not been possible for use on pulp fibers. An important feature also disclosed by the patent is that the salts are cationic and are, therefore, absorbed by the anionic cellulosic fibers.
Numerous sizing agents are known. Generally, the known sizes are cationic materials. Although the sizes' cationic nature increases their absorption by the fibers to which they are applied, their cationic nature generally prevents them from being used to the full extent possible in connection with a brightener and opacifying agent. It is well known in the art that although cationic materials often increase sizing, they have the disadvantage that they reduce the brightness of the material to which they are applied. The use of cationic sizes in the paper industry reduces the quality of the paper made therefrom. Because the addition of cationic sizing agents to paper generally reduces the brightness thereof, cationic sizes have not been preferred as a size for paper, and in particular, as a size for paper made from recycled pulp which often lacks the inherent brightness of paper made from virgin pulp.
Although the prior art shows agents for sizing paper and agents for increasing the brightness and opaqueness of paper, the particular features of the present invention are absent from prior art. The prior art is generally deficient in affording a composition for use in a papermaking process that has the ability to provide sizing to paper without reducing brightness or opacity.
The different US patents related to U.S. Pat. No. 5,296,024 indicate that the resulting amide of the diamine, which forms the cationic softener base, is the fatty acid monoamide or the diamide or a mixture thereof.
It is further indicated that the diamides are preferred to the monoamide and it is indicated that the diamides are more active cationic bases, and have stronger affinity for the cellulosic fibers to which they are absorbed (U.S. Pat. No. 5,296,024).
In this instance of a monoamide, however, the monoamide is the monoamide of a diamine. U.S. Pat. No. 5,488,139 describes an opacifier which is a reaction product of an alkanol amine and a dimerized acid, wherein the diamine (aminoethylethanol amine) is preferred, in this atent, the principal reactant with the amine is a dimerized acid.
U.S. Pat. No. 2,772,967 describes a size produced by reaction between a fatty acid and water soluble dialkanol amine or trialkanol amine. Thus, the reactants in the patent are a fatty acid and a monoamine. In this patent, however, the objective appears to be to perform an esterification reaction to produce esters between the fatty acid and the alcohol groups rather than amides between the fatty acid groups and the amine group.
U.S. Pat. No. 2,772,967 refers only to an esterification product as a sizing agent and not as an opacifier.
U.S. Pat. No. 5,296,024 indicates that concentrations greater than 5% were not possible with the sizing agents made by esterification mentioned in U.S. Pat. No. 2,772,967.